David from Animorphs after he is trapped as a rat.
An unintentionally hilarious example is seen at the end of Marianne Curley's The Key, where Ethan screams it after his true love Rochelle takes a magic arrow to the chest for him. Rochelle, who is narrating the story and using present tense, is able to tell us that the last thing she hears before she dies is Ethan screaming "Nooooo!"
In the first Wild Cards book (from 1986), Dr. Tachyon shrieks "Noooooooooooooooooo!" when he believes he has failed to prevent his friend Angelface from being shot.
In George R. R. Martin's A Clash of Kings ship-captain Davos Seaworth unleashes one of these during the bloody naval assault on King's Landing, when he realizes that one of the other attacking ships is about to set off a particularly nasty trap.
The Gaunt's Ghosts novel The Guns of Tanith uses this at the climax when Mkoll kills Sagittar Slaith.
Ron gets another one in Deathly Hallows after he hears Bellatrix give Greyback permission to kill Hermione.
Starcraft: Ghost: Nova. The title character does one of these every other page, just about. The other pages, somebody else fills in for her.
In Warrior Cats, Bluestar (then Bluepaw) bursts into one of these when her mother is killed in battle, complete with eight O's.
In The Hobbit, Gandalf tells Bilbo about Beorn and says that he is a 'skin-changer.' Bilbo expresses his thoughts by asking whether he meant 'furrier', to which Gandalf responds: 'Good gracious heavens, no, no, NO, NO!'
" Rikash - no! someone cried in a voice that cracked as it rose. "No! No! NOOOOO!" It was her voice. If she screamed loud enough, long enough, he would live. She hadn't realized that he meant something to her. She hadn't realized he was her friend."
Fandomar gets one with multiple "N"s in Galaxy of Fear, when she sees that The Virus has escaped. Though she doesn't tell anyone that that's what the empty room means.
Defied by Ciaphas Cain in Caves of Ice, at least according to his narration, when he's asked about whether his group should examine a tunnel probably leading to some Necrons: "'No.' It took all the self-control I could muster to sound calm and collected, instead of screaming the word."
After Mr. Click's leg comes off in A Bad Day For Voodoo, Tyler and Adam go to Tylerís house to watch the news, and the reporter announces that Mr. Click is dead. Adam shouts, "No!".